This invention relates to a porous ceramic combustion reactor used in combustion heating systems and more particularly to an outer surface design for a hollow porous ceramic reactor.
Gas fired porous ceramic reactors for generating an intense heat have been known and used for an appreciable period of time. A radiant gas burner incorporating such a reactor is described in the U.S. Pat. No. 3,191,659, issued June 29, 1965. Another is described in connection with a space heater in U.S. Pat. No. 3,179,156, issued Apr. 20, 1965. Characteristically, such reactors in operation exhibit an outer surface temperature of between 925.degree. C. to 1000.degree. C. These reactors are generally tubular and may have an inner surface temperature of about 65.degree. C. These reactors are ceramic and have low thermal conductivity. This low thermal conductivity in combination with the cooling effect of the flow of the gas and air mixture through the reactor from the interior outward, results in a concentration of heat in a thin outer surface layer about 0.5 mm thick. The elevated temperature of this surface layer causes it to shrink up to four percent (4%). The underlying material, not being nearly so hot, does not shrink measurably. Thus, the underlying material cannot accommodate to the surface shrinkage and as a result cracks appear on the surface. These cracks tend to appear as lines along a circumference. That is the crack lines are in planes that are substantially at right angles to the axis of the reactor. These cracks vary in depth and interval and often result in the scaling of the surface of the reactor.
Accordingly, it is a purpose of this invention to provide a ceramic reactor which can stand up to this differential temperature without substantial scaling.